Excerpts from Jim Conrad's
Naturalist Newsletter

from the July 12, 2015 Newsletter issued from Río Lagartos, on the north-central coast of Yucatán, MÉXICO
MEXICAN PRIMROSE-WILLOW

In mud and shallow water at the edges of ponds, lagoons and in ditch bottoms, nowadays you find knee-high herbs with pink stems and willow-like leaves, and bearing fair-sized, brightly yellow flowers, each blossom bearing four petals, as shown below:

Mexican Primrose-Willow, LUDWIGIA OCTOVALVIS

Up close, the flowers display a very distinctive architecture, as shown below:

Mexican Primrose-Willow, LUDWIGIA OCTOVALVIS, flower from front

There you see stamens clustered about the base of a thick style topped with an oversized, spherical stigma. Bases of the four petals -- and four is a somewhat unusual petal number -- are widely separated from one another, the stamens rising up between them. In the above picture you don't see an ovary because in this family, the Evening Primrose Family or Onagraceae, ovaries are "inferior." That means that the ovaries are located below the petals and male parts. Below, you can see the long, reddish, stem-like ovary below our flower, with four green sepals below and between the petals:

Mexican Primrose-Willow, LUDWIGIA OCTOVALVIS, flower from rear, showing sepals

While I was photographing the flowers a Toltec Roadside-Skipper, Amblyscirtes tolteca, suddenly landed on one, poked its straw-like proboscis around the style and began taking nectar from nectaries between the stamen bases -- while two mating flies supped on the other side -- as seen below:

Mexican Primrose-Willow, LUDWIGIA OCTOVALVIS, with insects taking nectar

In the US often wildflowers in this wildflower's genus, the genus Ludwigia, are called seedboxes because the ovaries mature into boxy capsules filled with tiny, hard seeds, which spill out when mature. They're also called primrose willows because their leaves are so willow-like. Our plant is the Mexican Primrose-Willow, LUDWIGIA OCTOVALVIS, apparently native to the tropical Americas, but found worldwide in tropics and subtropics, including the US Deep South. With such an extensive distribution, the "Mexican" part of the common name is appropriate only from the US point of view. When you think about the plant's tiny seeds mixed in mud that's likely to stick to the feet of wandering and migrating birds, the species' worldwide distribution becomes understandable.

The online Atlas de las Plantas de la Medicina Tradicional Mexicana reports that in parts of Mexico the plant is used for various skin diseases, including mange on animals. Also a tea made of brewing the plant in hot water is diuretic -- makes you pee.